TMD monolayers are atomically thin semiconductors having direct bandgaps. These monolayers are useful for various types of semiconductors such as photodetectors, optical modulators, solar cells, light-emitting diodes (“LED”), flexible displays, transparent displays, etc. Although there are various useful applications for monolayer and heterostructure TMDs, current chemical vapor deposition methods cannot be used for the growth of large TMDs or over other TMD layers.
Typical current techniques for TMD heterostructure fabrication use a transfer process. According to such a process, each TMD monolayer is grown separately and one monolayer is taken off of the growth substrate and stacked on the other monolayer. However, this transfer process is time-consuming, requires alignment when one monolayer is stacked onto another (which is problematic for some optoelectronics applications), and involves the use of polymers which contaminate the interfaces of resulting TMD heterostructures. While techniques for direct growth of heterostructures exist, such techniques have limitations in terms of their achievable size of heterostructures. Furthermore, only bilayered heterostructures have been demonstrated because such techniques cannot add another layer atop bilayered heterostructures since the materials are either evaporated or damaged during the growth of a subsequent layer.